Volume-targeted versus pressure-limited ventilation in the neonate

Abstract

Inflammation caused by lung overdistension (volutrauma) is thought to be important in the pathogenesis of bronchopulmonary dysplasia (BPD). Preterm infants with variable lung compliance are particularly at risk. Volume-targeted neonatal ventilators have been developed as alternatives to traditional pressure-limited ventilators. They deliver consistent, appropriate tidal volumes with the aim of reducing lung damage. It is suggested that these would provide an effective, safer means of ventilating the newborn infant. To determine whether volume-targeted ventilation compared with pressure-limited ventilation leads to reduced rates of death and BPD in newborn infants. Secondary objectives were to determine whether use of volume modes affected clinical outcomes such as incidence of airleak, growth, duration of ventilation or cranial ultrasound findings. The search strategy comprised searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2004), MEDLINE PubMed 1966 to November 2004, and hand searches of reference lists of relevant articles and conference proceedings. All randomised and quasi-randomised trials comparing the use of volume-targeted versus pressure-limited ventilation in neonates in the first 28 days of life. Two authors assessed the methodological quality of eligible trials and extracted data independently. When appropriate, meta-analysis was conducted to provide a pooled estimate of effect. For categorical data the relative risk (RR) and risk difference (RD) were calculated with 95% confidence intervals. Number needed to treat was calculated when RD was statistically significant. Continuous data were analysed using weighted mean difference (WMD). Four randomised trials were identified that addressed the outcomes of this review, recruiting a total of 178 preterm infants. All were recruited during the first 72 hours of life. Caregivers and those evaluating the outcomes of trials were not masked. All trials report high rates of follow-up, although one trial with uneven patient distribution may have had some post-randomisation attrition. No significant difference was found for death by hospital discharge, and no trials reported the combined outcome of death or BPD. When secondary outcomes were examined, pooled analysis of the trials showed that volume-targeted ventilation resulted in significant reductions in duration of ventilation [WMD -2.93 days (-4.28, -1.57)] and rates of pneumothorax [typical RR 0.23 (0.07, 0.76), RD -0.11 (-0.20, -0.03), NNT 9]. There was also a significant difference in rates of severe (Grade 3 or 4) intraventricular haemorrhage favouring the volume-targeted group [typical RR 0.32 (0.11, 0.90), RD -0.16 (-0.29, -0.03), NNT 6]. There was a reduction in the incidence of BPD (supplemental oxygen at 36 weeks) amongst surviving infants, of borderline statistical significance [typical RR 0.34 (0.11, 1.05), RD -0.14 (-0.27, 0.00), NNT=7]. No significant differences were found for failure of mode of ventilation, use of neuromuscular paralysis, patent ductus arteriosus, airleak of any sort or pulmonary interstitial emphysema alone, cranial ultrasound abnormalities or periventricular leucomalacia. None of the trials addressed growth, death after discharge from hospital or neurodevelopmental outcome. Although rates of death and BPD were not significantly different between the two ventilator strategies, statistically significant effects favouring volume targeting were shown for some clinically important outcomes. However, the numbers of trials and infants randomised are small and further studies are required to confirm the role of volume targeting in neonatal ventilation.